Question

A triangle has side lengths of 18 cm, 80 cm, and 81 cm. Classify it as acute, obtuse, or right.

Answer 1

Answer:

The answer is:

C - Acute

Hope this helps :)

Step-by-step explanation:

Answer 2

81^2 = 18 ^2 + 80^
6561 = 324 + 6400
6561 = 6724
It is not a right angle, since 18^2 + 80^2 does not equal 81^2.
So,
Using The law of cosines:
The largest angle C is opposite to the side c.
Therefore, 
c^2 = a^2 + b^2 -2ab cosC 
Here,
 c^2 < (a^2 + b^2)
 cosC must be positive which makes C an acute angle.